Production of solid caustic



United States Patent Ofiice 3,114,590 Patented Dec. 17, 1963 igan Filed Get. 23, 1957, Ser. No. 691,930 1 Claim. (Cl. 1847.5)

This invention relates to a process for producing solid caustic in marketable form. More particularly, it relates to a process for continuously converting a stream of molten caustic into blocks of solid caustic.

Caustic (by which is meant caustic soda, caustic potash and the like) in solid form has utility and there is a demand for such. Thus, caustic is commercially obtainable in the form of flake, pellets, and in drums. In the latter instance, molten caustic is poured into the drums and then the drums are cooled. This, of course, is a batch operation. So far as we are aware, however, solid caustic is not available commercially, nor has it been continuously made, inthe form of blocks or slabs.

It is a general object of this invention, therefore, to find a process for preparing solid caustic in large blocks.

A more specific object of this invention is to provide the art with a process for continuously producing solid caustic in blocks suitable for packaging. As a specific aspect of this problem, it is a specific object of this invention to continuously produce solid caustic soda from molten caustic.

These and other objects which may appear as this specification proceeds are attained by our invention.

In summary, from an apparatus point of view, our invention comprises a pumping station, a cooling and extruding station, and a slicing or cutting station.

The pumping station comprises a pump capable of producing the requisite pressures in a conduit containing molten caustic. For this station we prefer to use a positive displacement pump for safety reasons and because of better control over the hydraulic pressure of the caustic.

The cooling and extruding station involves an extruder provided with cooling means. Preferably, the extruder comprises a tube with an inlet at one end into which the stream of molten caustic under pressure is introduced, and an outlet at the other end from which solid caustic emerges. The tube is manufactured from a material having a reasonably high coefficient of heat transfer as well as an adequate resistance to corrosion, such as nickel, cast iron, etc. The length of the tube, the cooling means, and the rate of fiow of caustic are selected so that the stream of molten caustic solidifies in the tube. As the caustic solidifies, the cross-sectional area of the caustic shrinks. This effect, along with the hydraulic force of the molten, solidifying, stream of caustic behind it, tends to prevent the caustic from freezing or adhering to the wall of the cooling tube and enables the solid caustic to be propelled forward.

To facilitate rapid and uniform cooling from the center to the outside of the liquid and then semi-solid stream of caustic, it is preferred to provide the inside of the tube with heat transfer fins which also function to crease or scribe the solid caustic. By suitable placement and construction of the fins, the solid caustic can be formed and scribed as desired so as to permit the final product, in the form of blocks, to be broken into portions of predetermined weight at the point and time of use. If the blocks are not subdivided at the time of use, the creases or scores are of advantage in that they tend to increase the rate at which the block goes into solution.

It is preferred, also, that the cooling tube be inclined upwardly in the direction of travel of the caustic in order to provide safe operation and to assure complete filling of the tube by the caustic. Horizontal placement of the tube will suffice, but, disadvantageously, at times the upper portion of the tube might not be filled with caustic whereby the final product may contain void spaces and therefore not be of uniform weight. Downward inclination of the cooling tube can be utilized but it is not preferred because of the possibility of loss of control over the rate of travel of the caustic and thus the rate of cooling; too slow a rate of cooling may give rise to only partially cooled caustic at the outlet of the tube and thus a safety hazard.

To further assist the passage of the solidifying caustic through the tube, it is proposed to subject the walls of the tube to vibration which, along with the continuous passage of the caustic through the tube, functions to keep the walls of the tube free of adhering caustic. Such can be accomplished by manufacturing the cooling tube out of nickel (which has the added advantage of being noncorrosive) or a similar metal of a magneto-strictive nature, and subjecting the tube to varying magnetic forces supplied as from an electromagnetic coil or the like.

The extruder tube can be cooled by flowing through a jacket encasing the tube a coolant, such as water and the like. For the most efficient operation the flow of coolant should be countercurrent to the passage of the caustic.

It is preferred that the extruder tube comprise at the infeed end thereof a section or molten caustic zone wherein comparatively little cooling takes place in order to reduce any possibility of freezing up the infeed conduit and the pump and to prevent the occurrence of voids in the solid end product. This is accomplished by displacing the cooling means a short distance from the infeed end of the tube.

The slicing or cutting station comprises means, such as a band saw and the like, for dividing the solid caustic into sections, the dimensions of which, in the direction of travel, can be as desired. It may also comprise means for conveying the caustic from the extruder to the slicing means and means for conveying the caustic sections to a packaging station.

Process-wise, for best results, the caustic should be delivered in the molten, anhydrous condition to the apparatus of this invention. A trace of water can be tolerated but the proportion of water should be as low as practicable since the higher the water concentration the more likely the packaging material is to be damaged under storage conditions.

Before turning to the drawings, it should be understood that as this invention may be embodied in several forms without departing from the spirit or essential characteristics thereof, the embodiments to be described with reference to the drawings are therefore illustrative and not restrictive, since the scope of the invention is defined by the appended claim rather than by the description 3 preceding them, and all changes that fall within the metes and bounds of the claim are intended to be embraced by the claim.

Turning now to the drawings, it will be observed that FIG. 1 is a diagrammatic side view of a preferred apparatus of this invention;

FIG. 2 is a cross-sectional view of the extruder, taken along the lines 22 of FIG. 1; and

FIG. 3 is a side, sectional view of a portion of the extruder of FIG. 1, which has been modified with an electromagnetic coil.

In more detail, and with reference to FIGS. 1 and 2, there is shown a molten caustic feed conduit leading to the suction side of a positive displacement pump 12 with a discharge conduit 14 to the infeed end of a watercooled extruder 16, which comprises an inclined tube formed by heat conductive walls 18. As shown, the interior of the tube is rectangular in cross-section. However, other cross-sectional shapes, such as a circular shape, can be used.

Encasing the tube is a jacket with a cooling water infeed conduit 22 at the caustic discharge end of the extruder and a cooling Water discharge conduit 24 at the end of the jacket adjacent the caustic infeed end of the tube. Each end of the jacket is joined to the tube, as by way of a welding (not shown) or the like, to form a water-tight seal. It will be observed that a short portion of the tube at the caustic infeed end of the tube is not surrounded by the cooling jacket. The interior of this portion of the tube forms a molten caustic zone.

Running the length of the portion of the tube surrounded by the jacket 20 are two descending heat transfer fins 26 and two ascending heat transfer fins 28. Each fin is triangular in shape with the base thereof integral with the tube wall 18. The center line of each fin is shown equally spaced from the center lines of the neighboring fins. These fins function to transmit heat from the interior of the caustic stream and of the solidified caustic and to scribe or score the solidifying caustic into sectionalized portions which may be of predetermined weight per unit volume.

Under operative conditions molten caustic is passed into the positive displacement pump 12 which in turn impels the molten caustic through the pump discharge conduit 14 into the molten caustic zone of the extruder 16. The hydraulic pressure produced by the positive displacement pump propels the molten caustic through the extruder from the molten caustic zone into the jacketed portion. Caustic in contact with the walls 18 and the heat transfer fins 26 and 28 gives up heat thereto and eventually solidifies in its travel through the tube. Because of the cooling fins, heat in the caustic is more evenly and more rapidly dissipated throughout the cross-sectional area of the stream and the length of the extruder may be shorter than otherwise.

The length of the extruder, rate of flow of caustic, rate of cooling and the cross-sectional area of the caustic stream are all interrelated factors in the solidification of the caustic. By suitable selection of these factors, caustic, impelled by the hydraulic pressure of the molten caustic entering the molten caustic zone, emerges from the discharge orifice 40 of the extruder as a continuous, solid mass. In a preferred embodiment, the discharge orifice 40 of the extruder 16 has approximately the same crosssectional area as the water-cooled solidification chamber and corresponds, in general, to the shape of said solidification chamber.

This continuous mass of solid caustic passes over rollers 30 or a chute to a sectionalizing station whereat the caustic is sliced by means of a circular or band saw 32 into slabs or blocks. The saw may travel across the caustic or down from overhead. It may move with the caustic or be synchronized with a momentary stopping of the pump 12.

The sections of caustic so obtained are then conducted i by a powered roller 34, belt conveyor and the like to a packaging station whereat they may be packed, for example, in polyethylene bags and cardboard cartons. The polyethylene bags can be over-Wrapped with waxed paper and the cardboard cartons can be of wax-coated stock.

The passage of the caustic through the extruder is facilitated by the shrinkage of the caustic in changing from the liquid to the solid state. Such passage may be further aided by vibrating the walls 18 of the tube. In FIG. 3, this concept is utilized by constructing the walls 18 of the tube out of nickel, by constructing the walls forming the jacket 20 out of a magnetically permeable material, and by surrounding the jacket with an electromagnet coil 36 associated with a source of alternating or interrupted electric current of high frequency.

One of the properties of nickel is that it will expand and contract when exposed to a varying magnetic field. Subjecting the extrusion tube to such a field increases the heat transfer rate by breaking loose from the wall 18 the adjacent layer of solidified caustic until the underlying mass has cooled and solidified, as Well as breaking loose crystals of caustic adhering to the wall. This embodiment has an advantage in that the necessary tube length can be less than the embodiment shown in FIG. 2, the flow rate of caustic can be increased, and/ or the flow rate of the cooling medium can be decreased.

Typical dimensions, flow rates and other conditions of operation contemplated in the embodiment of FIG. 1 are set forth as follows:

Length of extruder tube 50 feet. Angle of inclination of tube- 10. Width in cross-section of tube 10 inches. Height in cross-section of tube 1% inches. Length of molten caustic 1 zone 1 foot. Depth (and height) of heat transfer fins 1 inch.

The continuous mass of caustic so produced is sliced into slabs 12 inches long (10 inches wide and 1% inches high) which weigh about 12 /2 pounds.

In the fll'GOV table, and generally speaking, the pump will be normally openated to produce pressures up to about psi. However, it should be capable of higher pressures in case abnormal freeze-ups, increased friction caused by bent heat transfer fins, etc. are encountered, and for these reasons up to 1000 psi. has been specified.

ie embodiments of the drawings have another advantage in that in case the extruder l6 freezes up as may happen during start-ups or plant interruptions, the frozen caustic can be liquefied by running hot water or steam through the jacket 20 for short intervals of time, until the machine is in normal operation.

What is claimed is:

A process for continuously producing solid caustic blocks from molten caustic, which comprises pumping molten caustic through an enclosed path containing in sequential communication an inlet orifice, a molten caustic zone, a caustic solidification zone and a discharge orifice, said discharge orifice having a cross-sectional area approximately the same as the cross-sectional area of said caustic solidification zone, cooling said molten caustic in said caustic solidification zone to thereby form solid caustic, scribing said caustic with heat transfer fins during 5 its travel through said caustic solidification zone whereby said bar of caustic is solidified on the inside and scribed in portions of predetermined weight and density, passing said solid caustic through said discharge orifice and slicing said solid caustic into blocks.

References Cited in the file of this patent UNITED STATES PATENTS 2,204,737 Swallow et a1. June 18, 1940 6 Gilbert et a1 Sept. 30, Van-g Aug. 14, Shaw Jan. 26, Henrich July 26, Johnson June 19, Walters Sept. 4, E lssner July 23, Bauer Aug. 6,

Davis Aug. 13,

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent Noe 3,114 59O December 17, 1963 Jean M, Hoff et a1.

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 1 lines 30 to 48 should appear as shown below instead of as in the patent:

Length of extruder tube 50 feet,

Angle of inclination of tube 10 0 Width in cross-section of tube 10 inches,

Height in cross-section of tube 1-3/4 inches Length of molten caustic zone 1 foot,

Depth (and height) of heat transfer fins 1 inch,

Thickness of fin at base 1/4 inch,

Distance between adjacent center lines of fins 2-l/2 inches,

Flow Rate of molten anhydrous casutic;

soda at 650 F. 3/4 ton per hour Discharge Temperature of solid caustic about 200 F,

Pump pressure up to 1000 p,s,i.

Signed and sealed this 19th day of January 1965.

(SEAL) Attest:

ERNEST W. SWIDER EDWARD J. BRENNER Attesting Officer Commissioner of Patents 

